Deconvolving light absorption properties and influencing factors of carbonaceous aerosol in Shanghai

Insight into the abundance and optical characteristics of water-soluble organic compounds (WSOC) in PM2.5 in urban areas

Airborne particulate matter (PM) poses significant environmental and health challenges, particularly in urban areas. This study investigated the characteristics of water-soluble organic compounds (WSOC) in PM2.5 (PM with an aerodynamic diameter of 2.5 μm or less) in Singapore, a tropical Asian city-state, over a six-month period. Specifically, we examined the abundance, optical properties, and fluorescence characteristics of WSOC in PM2.5 collected from various urban locations, employing complementary instrumental techniques, parallel factor (PARAFAC) modeling, and Kohonen's self-organizing map (SOM). Our findings highlight that the differences in WSOC characteristics between sites reflect the influence of primary emissions of PM and secondary PM formation processes. Concentrations of PM2.5 and WSOC on roadsides are influenced by vehicular traffic composition and volume. Under conducive atmospheric conditions, volatile organic compounds (VOCs) from vehicle emissions are oxidized to form WSOC, with its chemical composition dependent on whether oxidation occurs in the gas or aqueous phase. The findings also indicate that while vegetation barriers (VBs) planted along the roads in this study do not significantly reduce PM2.5 concentrations, they alter the chemical composition and light absorption properties of WSOC. The capacity of VBs to retain PM less than 1 μm in size shows their potential in reducing exposure to harmful traffic emissions. Moreover, fluorescence analysis revealed the presence of humic-like and protein-like compounds, underscoring the complex chemical nature of WSOC. This study provides a comprehensive insight into the molecular composition and properties of WSOC in PM2.5.

An investigative review of the expanded capabilities of thermal/optical techniques for measuring carbonaceous aerosols and beyond

Carbonaceous aerosols primarily comprise organic carbon (OC) and black carbon (BC). Thermal-optical analysis (TOA) is the most commonly used method for separating carbonaceous aerosols into OC and EC (BC is referred to as elemental carbon EC, in this method). Advances in hardware design and algorithms have expanded the capabilities of TOA beyond just distinguishing OC and EC. However, a comprehensive understanding of the enhanced functionality of TOA is still lacking. This study provides the first comprehensive review of the TOA technique, highlighting expanded capabilities to measure brown carbon (BrC), mass-absorption efficiency, absorption enhancement, source contributions, and refined OC/EC split points. This review discusses the principles, advantages, and limitations of these advancements. Furthermore, the TOA system anticipates further advancements through integration with other instruments, establishing correlations between EC values obtained from different TOA instruments/protocols, correlating between BrC measurements from TOA and non-TOA methods, and developing an algorithm to quantify BrC from progressive absorption Ångström exponent (AAE) values. This review enhances the understanding of the TOA system and its implication for air quality and atmospheric radiation research.

Research progress on the characteristics, sources, and environmental and potential health effects of water-soluble organic compounds in atmospheric particulate matter

Water-soluble organic compounds (WSOCs) have received extensive attention due to their indistinct chemical components, complex sources, negative environmental impact, and potential health effects. To the best of our knowledge, until now, there has been no comprehensive review focused on the research progress of WSOCs. This paper reviewed the studies on chemical constituent and characterization, distribution condition, sources, environmental impact, as well as the potential health effects of WSOCs in the past 13 years. Moreover, the main existing challenges and directions for the future research on WSOCs were discussed from several aspects. Because of the complex composition of WSOCs and many unknown individual components that have not been detected, there is still a need for the identification and quantification of WSOCs. As modern people spend more time in indoor environments, it is meaningful to fill the gaps in the component characteristics and sources of indoor WSOCs. In addition, although in vitro cell experiments have shown that WSOCs could induce cellular oxidative stress and trigger the inflammatory response, the corresponding mechanisms of action need to be further explored. The current population epidemiology research of WSOCs is missing. Prospectively, we propose to conduct a comprehensive and simultaneous analysis strategy for concentration screening, source apportionment, potential health effects, and action mechanisms of WSOCs based on high throughput omics coupled with machine learning simulation and prediction.